Milling head cutters

ABSTRACT

A milling head for forming globoid worms, having two sets of cutting instruments. One set of cutters is fixed. The other set is removable. The cutting edges are arranged along specific axes and directions to effect cutting.

[ 1 Jan. 23, 1973 [56] References Cited UNITED STATES PATENTS 1,903,9884/1933 Pickett.............. 2,881,508 4/1959 FOREIGN PATENTS ORAPPLICATIONS 1,142,008 3 1957 France 396,339 8/1933 Great Britain...

420,931 5/1947 Primary Examiner-Harrison L. Hinson Attorney-Richard Lowet a1.

[57] ABSTRACT A milling head for forming globoid worms, having two setsof cutting instruments. One set of cutters is fixed. The other set isremovable. The cutting edges are arranged along specific axes anddirections to effect cutting.

5 Claims, 2 Drawing Figures Strejc, Plzen,

podnik, Plzen,

.29/105 R, 90/1 .B26d l/l2 .29/95, 103 R, 103 B, 105 R, 29/105 ABohuslav Czechoslovakia Skoda, narodni Czechoslovakia Nov. 18, 1971Appl. No.: 200,096

Related US. Application Data [63] Continuation of Ser. No. 888,645, Dec.29, 1969,

Foreign Application Priority Data Dec. 29, 1968Czechoslovakia...................

Field of Search Inventor:

[73] Assignee:

[22] Filed:

Pat. No. 3,621,755.

United States Patent Strejc MILLING HEAD CUTTERS MILLING HEAD CUTTERSThis is a continuation of Ser. No. 888,645 filed Dec. 29, 1969 now U.S.Pat. No. 3,621,755 issued Nov. 25, 1971. 7

BACKGROUND OF INVENTION This invention relates to the arrangement of amultiknife milling head for the manufacture of worm wheels andparticularly of globoid worm wheels.

Known manufacturing methods of globoid worm wheels use generally,multiknife milling heads with knives, the cutting edges of which arearranged in accordance with the geometric laws of the globoid helix. Theknives are of equal shape and are permanently clamped in the millinghead. These knives advance in the course of rough milling radially inengagement with the workpiece which is in fact the semi-product of theworm wheel, performing the rough milling with the same cutting edges asis used to subsequently finish the piece after the proper axial distancebetween the tool and workpiece is obtained. As a result a limitedcircumferential feeding motion between the tool and the workpiece isaccomplished. The cutting edges at both extremities of the milling headthus become quickly worn and the required quality of the surfaces of thetooth flanks, particularly of the surfaces which are in engagement withthe worm, is not achieved during the finishing operation. Consequently,not all the material is removed and metal of the thickness of severalhundreth parts of a millimeter remains on these engaging surfaces, justas it does on parts which do not come into engagement. It has,therefore, been necessary to frequently sharpen the cutting edges of themultiknife milling head, reducing thus the life time of the tool andincreasing its maintenance costs.

Another conventional arrangement of a milling head is described in theGerman Pat. specification No. 673,400 where two internal removableknives are provided in addition to permanently fixed cutting knives. Theremovable knives perform the finishing operations only, whereas thepermanently clamped knives work in the course of the whole workingprocess. The active cutting edges of these knives are adjusted so as tocomply with the width of the tooth gap and all cutting edges are on thesame helical surface as the removable knives. The finishing is performedwith all knives which form the whole tooth gap and all knives areadjusted alike. The main knives are the external knives, usedpermanently both for roughing and finishing. A shallow engaging surfacewhich is not worked completely is thereby created on the tooth flanks ofthe worm wheel. The milling head arranged in this manner only reducedthe drawbacks of milling heads with all knives permanently clamped,reducing somewhat the time required for running-in the worm gear. Thesubstantial drawback, the quick wear of cutting edges of the millinghead has however, not been eliminated. The better final result ofmilling has been compensated for by high wear of knives on bothextremities of the milling head which after only two or three millingoperations have lost their life. This drawback shows up when theengaging surfaces of the finished gear do not properly work.

It is the object of the present invention to overcome the drawbacks ofthe prior art; to provide an improved method and apparatus for forminggloboid gears, and to provide improved method and apparatus forsimplifying cost and labor involved in the same.

These and, additional objects and advantages will be apparent from thefollowing disclosure.

SUMMARY OF INVENTION According to the present invention, a multiknifemilling head is provided comprising in addition to permanently clampedknives two removable knives, arranged in the body of the multiknifemilling head so that the position of their cutting edges for cutting thetooth flanks coincide at least in one point with a theoreticalgenerating line which is perpendicular to the rotation axis of the tool,whereas parts of cutting edges of all knives of the milling headdesignated for milling the tooth gaps are in a position corresponding tothe root circle of the worked worm wheel. The position of parts ofcutting edges of the removable knives for cutting tooth flanks coincidewith the theoretical position of a generating line of the worm gearcorresponding to the width of the tooth of a worm having no clearancewith the teeth of the worm wheel, whereas the position of similar partsof permanently clamped knives coincide with generating linescorresponding to a smaller width of the teeth of the worm.

It is furthermore, preferred that the position of the cutting edges ofthe removable knives for roughing the tooth flanks comply with thetheoretical position of the generating line of the globoid gear, whereasthe position of analogical cutting edges of the permanently clampedknives are identical with the actual dimensions of the tooth flanks ofthe helical surface of the worm, for which the worm wheel ismanufactured.

It is further preferred to use this arrangement to create conditions,where the working of the worm wheel proceeds within two subsequentworking phases, a preliminary phase and a finishing phase. The removableknives perform together with permanent knives the rough milling withparts of their cutting edges which cut the gaps between adjacent teethup to the root circle of the worm wheel. At the end of this preliminaryphase these removable knives make the rough milling of the tooth flankswith the respective parts of their cutting edges.

Full details of the present invention will be seen from the followingdescription and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a side view of a milling head showing its construction andalso schematically the basic parameters of a globoid worm gear andmultiknife milling head, and

FIG. 2 is a cross section taken along the plane indicated by line 5 inFIG. 1.

DESCRIPTION OF THE INVENTION The body 10 of the multiknife milling headhas substantially the fundamental shape of a globoid worm. Therotational axis 4 of the body l0 of the milling head is, for thefinished roughing operation located at the distance 9 from the axis ofthe worm wheel which axis is coincident with the center S of thegenerating circle 1 of the worm gear. The distance 9 is measured on aradial line of the generating circle 1 perpendicular to the axis 4, andis also coincident with the proper distance of the axis of the worm andworm wheel in operation. The multiknife milling head is provided withtwo kinds of knives. The first kind are knives 2 and 3 and are locatedat the ends of the tool and are removable. They have a cutting edge 1 lfor roughing the tooth flanks of the worm wheel which is adjusted independence on the extreme position of the generating line 7 of thegloboid worm gear. The generating line is a tangent to the generatingcircle 1 of a diameter 8 and simultaneously perpendicular to the axis 4of the milling head. The position of the cutting edges 11 of theremovable knives 2, 3 is thus determined by the generating laws of thegloboid helix of the globoid worm gear in accordance with conditionscorresponding for instance, to values on the pitch circle 6 of thegloboid gear. It takes into account equally possible requirements whichfollow from multithreaded worms. That means that the position of thecutting edges for the tooth flanks corresponds to the theoreticalposition of the generating line and meets all the parameters of themanufactured globoid gear by their arrangement in the body of themultiknife milling head.

in conventional manner a set of permanently secured knives 14 are set inthe face of the milling body 10 so that their cutting edges lie in aposition corresponding to the root circle 13 of the worm wheel. Thisstructure and arrangement is well known and therefore need not befurther described.

The cutting edges 11 of the removable knives 2, 3 can be sharpenedbefore insertion in or even on their removal from the body 10 of themilling head so as to maintain the correct shape and cuttingangle. Theyare inserted into the body 10 so that the lead portions 12 of thecutting edges which cut the tooth gaps are in a position correspondingto the root circle 13 of the worm wheel, similarly as are the cuttingportions of the permanently clamped knives 14. The permanently clampedknives 14 are each mounted in openings 16 in the body 10 of themultiknife milling head. These openings 16 are arranged in directdependence on the theoretical globoid helix l5 and generally in severalrows. An exemplary arrangement is indicated in FIG. 2. The permanentlyclamped knives 14 are supported in openings 16 of the body 10 of themilling head, whereby the axis of these knives point angularly in adirection determined by a circle of the diameter 8, which is in theplane of symmetry of the body 10 perpendicular to its axis 4, saidcircle touching for a finished working the axis 5 of the worm wheel. Theopenings 16 are bored in direct dependence on the theoretical globoidhelix l5 and their axis are generally arranged in several rows laying ina number of plans, passing through the axis 4 of the milling head. Theyare secured in the body 10 in the usual manner by laterally actingscrews. in FIG. 2 showing a vertical cross sectional view of the body 10of the milling head there are four such planes 1, 11, 11], 1V in whichthe axis of the knives 14 are arranged. The removable knives 2, 3 areadvantageously beyond said planes 1 to 1V. The permanently clampedknives 14 have such a width, that they do not come in the course ofroughing in contact with the tooth flanks which are worked by theremovable knives 2, 3. If some modification of the tooth flanks is used,the cutting edges of the knives are adjusted according to theserequirements, but at any case at least one point of the cutting edge 11for roughing the tooth flanks is on the generating line 7, which is atangent to the generating circle 1 and perpendicular to the axis of themilling head.

The described arrangement works as follows. The multiknife milling headis clamped in a machine tool for milling teeth operated on the hobbingprinciple, on the worktable of which the workpiece of the globoid wormwheel is fixed. The rotating speeds of the milling head and of the wormwheel are adjusted according to the transmission ratio of the requiredgloboid worm gear. The rotating workpiece is subsequently, in the courseof working, brought radially into engagement with the knives of therotating milling head, to a distance corresponding to the correct axialdistance 9 of the worm from the worm wheel. In this working phase theroughing is finished and thereafter the machine is stopped. Theremovable knives 2, 3 are then removed, and the workpiece receives withrespect to the milling head a small circumferential turn in direction 17and the first tooth flanks 18 of the globoid worm wheel finished by thepermanently clamped knives 14. After a small turn of the workpiece withrespect to the milling head in the opposite direction 20, the secondtooth flanks 19 of the worm wheel are finished.

An advantage of the arrangement according to this invention is the longlife of the cutting edges of the permanently clamped knives of themultiknife milling head as the removable knives perform the roughingboth with the cutting edges which cut the tooth gap up to the rootcircle and with cutting edges, cutting the tooth flanks, which lattercutting edges comply with the theoretical position of the generatingline of the gear, whereas the permanently clamped knives perform theroughing solely with cutting edges cutting the tooth gap up to the rootcircle, whereas the cutting edges for cutting the tooth flanks performsolely the finishing after a limited circumferential feeding motion, sothat they are capable to be used for a considerable time.

The multiknife milling head according to this invention eliminatestherefore, existing drawbacks as regards the shape and quality of theengaging surfaces of tooth flanks of globoid worm wheels in the courseof their finishing. The thus manufactured globoid gear shows perfectengaging surfaces, smooth running, high efficiency and a possibility offull load without tedious breaking in.

The removable knives are easily sharpened to the theoretical valueoutside the milling head and then clamped in the milling head so thattheir edges coincide with a generating line of the globoid gear which isperpendicular to the rotation axis of the tool (or of the resultantworm). The permanently clamped knives are inserted similarly, theiredges, however, comply with the corresponding position of the generatingline. The width of these permanently clamped knives is smaller than thetheoretical width of the tooth gap of the worm wheel which has to befinished with these knives. In the thus arranged milling head thecutting edges for tooth V flanks of the removable knives, which are on ahelical surface determining the tooth flanks, are more distant one fromthe other than cutting edges for tooth flanks of permanently clampedknives. In the course of roughing (that is, in the course of feeding ofthe tool up to the axial distance of the gear) they do not cut, as theyare on a helical surface corresponding for instance, to a helicalsurface shifted for the supposed clearance of tooth flanks between theworm and the worm wheel. As these cutting edges do not take part in theroughing step, they are capable of use to finish the shape of theengaging surfaces of successive tooth flanks for a considerable time.

The roughing is therefore, performed by parts of all knives, but ofcourse, only up to the moment, where the working has reached the rootcircle of the globoid worm wheel. The parts of teeth which are inoperation out of engagement are thereby milled, with a followingfinishing of the tooth flanks at places of engagement, which isperformed by the respective cutting edges of the permanently clampedknives. This creates perfect engaging surfaces, corresponding in shapeto the globoid worm, whereby said surfaces are already worked up to adepth, corresponding to the correct engagement. A similar working of theengaging surfaces enables the reduction of the time needed to break inthe gear to a significantly short time and at nominal loads and atnormal efficiency. The life time of the cutting edges of the millinghead used for finishing, that is of the permanently clamped knives ismany times increased.

lt will thus be observed that the objects aforementioned are allobtained by the present invention and that a simple efficient system isobtained to overcome the defects of the prior art. Various changes andmodifications are permissable and will be obvious to those skilled inthis art. It is, therefore, intended that the present description beillustrative only and not limiting of the present invention.

What is claimed:

1. A multiknife milling head for the manufacture of worm wheelscomprising a body, a plurality of knives permanently clamped to saidbody, a pair of removable knives arranged in the body so that thepositions of their cutting edges for cutting the tooth flanks coincideat least in one point with a theoretical generating line which isperpendicular to the rotation axis of the body, at least portions of thecutting edges of all knives designated for milling the teeth beinglocated in a position corresponding to the root circle of the workedworm wheel.

2. A multiknife milling head as set forth in claim 1 wherein theposition of the portions of the cutting edges of the removable knivesfor cutting tooth flanks coincide with the theoretical position of agenerating line of the worm gear corresponding to the width of the toothof a worm having no clearance with the teeth of the worm wheel, theposition of similar parts of the permanently clamped knives coincidewith generating lines corresponding to a smaller width of the teeth ofthe worm.

3. The apparatus according to claim 2 wherein said body has the shape ofa globoid worm, said removable knives are located at the axial endsthereof, said permanently clamped knives are located about thecircumferential face of said body.

4. The apparatus according to claim 3 wherein the radial extent of saidremovable knives from the circumference of said body exceeds that ofsaid permanently clamped knives.

5. A method of forming globoid wheels having teeth of a defined rootcircle, comprising the steps of locating a rotating body adjacent agloboid workpiece, arranging on said body a first set of removable teethand a second set of fixed teeth, the removable knives extending beyondsaid body a distance greater than the distance of said fixed knives,working said workpiece until said removable knives reach the root circleof the teeth, removing the removable knives and continuing working saidworkpiece until said fixed knives reach the root circle.

1. A multiknife milling head for the manufacture of worm wheelscomprising a body, a plurality of knives permanently clamped to saidbody, a pair of removable knives arraNged in the body so that thepositions of their cutting edges for cutting the tooth flanks coincideat least in one point with a theoretical generating line which isperpendicular to the rotation axis of the body, at least portions of thecutting edges of all knives designated for milling the teeth beinglocated in a position corresponding to the root circle of the workedworm wheel.
 2. A multiknife milling head as set forth in claim 1 whereinthe position of the portions of the cutting edges of the removableknives for cutting tooth flanks coincide with the theoretical positionof a generating line of the worm gear corresponding to the width of thetooth of a worm having no clearance with the teeth of the worm wheel,the position of similar parts of the permanently clamped knives coincidewith generating lines corresponding to a smaller width of the teeth ofthe worm.
 3. The apparatus according to claim 2 wherein said body hasthe shape of a globoid worm, said removable knives are located at theaxial ends thereof, said permanently clamped knives are located aboutthe circumferential face of said body.
 4. The apparatus according toclaim 3 wherein the radial extent of said removable knives from thecircumference of said body exceeds that of said permanently clampedknives.
 5. A method of forming globoid wheels having teeth of a definedroot circle, comprising the steps of locating a rotating body adjacent agloboid workpiece, arranging on said body a first set of removable teethand a second set of fixed teeth, the removable knives extending beyondsaid body a distance greater than the distance of said fixed knives,working said workpiece until said removable knives reach the root circleof the teeth, removing the removable knives and continuing working saidworkpiece until said fixed knives reach the root circle.